The present invention relates generally to integrated circuits and, more particularly, to driver circuits for integrated circuit pads.
Integrated circuits process input signals and generate output signals. To communicate with the outside world, integrated circuits have I/O pads, which allow for connection to external devices. Thus, integrated circuits usually include both a data transmitter or driver circuit, and a receiver circuit. Communicating data signals can be complicated and is the subject of extensive studies relating to transmission lines. To reduce data signal ringing and signal interference, the rise time or slew rate of a signal transmitted on a bus is often controlled.
Continued reduction of integrated circuit sizes has led to a corresponding lowering of voltage supply levels and the use of low voltage devices. However, the peripheral circuits and I/O supply levels continue to operate at higher voltage supply levels. For example, a bus driver circuit may operate at 3.3V, but the fabrication process may not support such high voltage devices. Operating the lower voltage devices at higher voltage levels leads to reliability issues like hot carrier injection, gate oxide, and source drain breakdown.
Accordingly, it is an object of the present invention to provide a transmission line driver circuit formed with low voltage devices, yet operable with a higher supply voltage without degrading device reliability.